1. Field of the Invention
The present invention concerns a miniature electronic component having variable self-inductance consisting of a coil associated with a movable ferromagnetic core the depth of penetration of which into the coil is adjustable.
2. Description of the Prior Art
To simplify the manufacture of this type of component and to improve its electrical specifications it is important to minimize the number of small parts additional to the coil and to the core, and in particular to avoid the use of any form of mounting base, connecting terminals, former supporting the winding, spacers by which the coil is mounted onto the base and other parts supporting the core and enabling it to slide.
From French Pat. No. 2,486,704 it is known to do this by using a winding of thermo-adherent wire with no coil support soldered to a pair of connecting skids stamped out from a metal strip and encapsulated in a cold cast and hot polymerized resin in a flexible mold through which passes a pin forming a partially threaded axial cavity to accommodate a movable core formed by a ferromagnetic rod with a grubscrew overmolded at one end.
This type of miniature inductor sometimes has surface defects: small craters due to air bubbles trapped along the walls of the mold when the resin is cast or unwanted protrusions due to deterioration of the flexible mold. Apart from the fact that such defects are unesthetic, they may compromise the quality of the component because they can generate pockets in which are retained corrosive products from the solder flux used when mounting the component.
Molding is hardly practicable since it entails individual centering of each component. The flexible mold shrinks when it is warmed on polymerizing the resin, which alters the distance between two successive component imprints and makes it necessary to use each pair of connecting skids separately, in other words to divide up the metal strip into which they are stamped instead of retaining the strip to benefit from the resulting easy centering. Also, the thread on the pin used to form the housing for the movable core is frequently soiled by resin residues which makes it necessary to carry out delicate cleaning and checking operations, given the small size of the part concerned.
An object of the present invention is to remedy these various disadvantages while retaining a low unit cost.